This paper investigates the matrix coupled "all-in-one"magnetic structure that combines both series coupling and parallel coupling for pulse-width-modulated (PWM) power conversion. A systematic analysis of the current ripple reduction mechanism is performed. The transient performance of the matrix coupled inductor is demystified, providing guidance on the analysis of converter dynamics and large- or small-signal modeling. To quantify the benefits of matrix coupling, a figure of merit is defined by comparing the current ripple of a matrix coupled inductor to that of a discrete inductor given the same transient speed. The comparison results indicate that a higher number of phases and a stronger matrix coupling coefficient amplify the benefits of matrix coupling. A 1 V-to-5 V input, 1 V-to-5 V output, four-phase matrix coupled synchronous SEPIC converter with planar PCB integrated magnetics was built and tested. The experimental results validate the matrix coupling concept and the theoretical analysis, opening the possibility towards wide adoption of "All-in-One-Magnetics"in PWM topologies.